The overall project aims to assess potential mechanisms on how exposure to air pollution leads to systemic effects consisting of increased lipid peroxidation, HDL dysfunction and enhanced atherosclerosis. Cumulative epidemiological and experimental data have shown that exposure to air pollutants leads to increased cardiovascular morbidity and mortality, especially of ischemic nature. We have found that exposures to diesel exhaust and ambient ultrafine particles (PM< 0.1 m) lead to dysfunctional HDL characterized by reduced antioxidant and anti-inflammatory vascular protective properties. The development of dysfunctional HDL correlates with increased lipid peroxidation in systemic tissues and increased formation of atherosclerotic lesions. We have also observed that diesel exhaust leads to activation of the 5-lipoxygenase (5-LO) pathway in the liver. In the last few years, remarkable progress has been made in determining a plethora of systemic effects induced by air pollution. Many mechanistic details remain to be elucidated how air pollution leads to atherosclerosis. Our overarching hypothesis is that exposure to ambient PM results in lipid peroxidation, dysfunctional HDL and enhanced atherosclerosis via the induction of systemic prooxidant and proinflammatory effects that are mediated by the activation of macrophages and lipoxygenase pathways. We have proposed to test this hypothesis via three specific aims. During the bridging period funded by the R56 award, the effort will be focused on obtaining data to strengthen specific aims 1 and 2, as follows: 1) To evaluate whether activation of the 5-LO pathway mediates air pollution effects on lipid peroxidation, HDL dysfunction and atherosclerosis. We will explore the connections between 5-LO and Heme oxygenase-1 (HO-1) expression as well as the expression of other lipoxygenases in lungs, liver, aorta from ApoE null mice exposed to Diesel exhaust vs. filtered air. This will allow us to achieve a strong mechanistic framework between 5-LO and HO-1. 2) To assess the role of alveolar and systemic macrophages in the enhancement of lipid peroxidation, HDL dysfunction and atherosclerosis induced by air pollutants. We will expose macrophage-specific HO-1 KO mice in the ApoE null background and control littermates to diesel exhaust vs. filtered air to evaluate the impact of macrophage deletion of HO-1 on lipid peroxidation, HDL dysfunction and atherosclerotic lesions, and determine the connections between HO-1 and 5-LO. We will also develop mouse lung chimeras with ablated HO-1 and decreased antioxidant defense in their alveolar macrophages. These mice have a fluorescent reporter that will enable us to track HO-1 null alveolar macrophages and detect their migration from the lungs into systemic vessels, which will allow us to test the role of these cells in mediating systemic effects induced by diesel exhaust in future experiments.